F-1031, Section 2449
Page 16 of 18
Pump (Continued)
Problem
Possible Cause
Recommended Action
Insufficient capacity
B.
Engine and pump
speed low at full
throttle
Transfer valve set improperly
(Does not apply to single
stage pumps.)
Place transfer valve in VOLUME (parallel) position when
pumping more than two thirds rated capacity.
When shifting transfer valve, make sure it travels all the way
into new position. Failure of transfer valve to move completely
into new position will seriously impair pump efficiency.
Pump impeller(s) or wear
rings badly worn
Install undersize wear rings if impeller to wear ring clearance
is within limits indicated in MAINTENANCE INSTRUCTIONS.
If not, install new impeller(s) and wear rings.
Intake strainer, intake
screens or impeller vanes
fouled with debris
Remove intake strainer and hose, and clear away all debris.
Pressure backwash (preferably in parallel or “volume”
position) will usually clear impeller vanes when pump is
stopped.
Intake hose defective
On old intake hoses, the inner liner sometimes becomes so
rough it causes enough friction loss to prevent pump from
drawing capacity. Sometimes, the liner will separate from the
outer wall and collapse when drafting. It is usually impossible
to detect liner collapse, even with a light. Try drafting with a
new intake hose; if pump then delivers capacity, it may be
assumed that previous hose was defective.
Intake hose too small
When pumping at higher than normal lifts, or at high altitudes,
use a larger or additional intake hoses.
Insufficient capacity
C. Engine and pump
speed low at full
throttle
Truck transmission in too low
a gear
Consult vehicle instructions for correct pumping gear.
Pump usually works best with transmission in direct drive.
(Check both engine and pump speed, if possible, to be sure
transmission is in “direct”.)
Insufficient pressure
Pump speed too low
In general, the above causes and remedies for low pump
capacity will also apply to low pump pressure.
Check pump speed with a tachometer.
If pump speed is too low, refer to engine manufacturer’s
instructions for method of adjusting engine speed governor.
Pump capacity limits pump
pressure
Do not attempt to pump greater volume of water at the desired
pressure than the pump is designed to handle.
Exceeding pump capacity may cause a reduction in pressure.
Exceeding maximum recommended pump speed will produce
cavitations, and will seriously impair pump efficiency.
Flap valve stuck open
When pump is in PRESSURE (series), discharge will bypass
to first stage intake. Operate pump at 75m PSI/52 bar, and
rapidly switch transfer valve back and forth between positions.
If this fails, try to reach valve with a stick or wire and work it
free.
Troubleshooting Guide
